Recently, a backside-illuminated image sensor has been introduced to an image sensor field. The backside-illuminated image sensor has an improved light-receiving efficiency, which is accomplished by having a wiring layer arranged on a front surface of a semiconductor substrate and by receiving light from a rear surface of the semiconductor substrate. In general, the backside-illuminated image sensor includes a backside-illuminated active pixel sensor array in which a plurality of pixels are arrayed in a matrix. Each pixel has a photodiode for receiving an optical signal incident via the rear surface of the semiconductor substrate and for converting the light signal into an electrical signal. However, in the backside-illuminated active pixel sensor array according to the related art, charges that are generated in a specific pixel move to a photodiode of an adjacent pixel thereby causing crosstalk.